Effect of Different Salinity Levels on Population Dynamics and Growth of the Cyclopoid Copepod Oithona nana

Abstract

Copepods are one of the most abundant and diverse live food sources for mesopelagic and bathypelagic fishes and crustaceans. They could contribute to the overlap of the transition period from live feed to an artificial weaning diet in marine larvae production. However, the culture conditions still need optimization to provide sufficient production to cover the increasing demand for marine hatcheries. Therefore, the present study investigated the effects of different salinity levels (5, 10, 15, 20, 25, and 30 ppt) on the population growth, growth rate, and population composition (males, females, copepodite, and nauplii ratio) of the marine copepod, Oithona nana. The experiment continued for 15 days, under laboratory-controlled conditions of temperature (27 ± 1 °C), pH (7.7 ± 0.15), and continuous gentle aeration in 30 L glass aquaria. The copepod culture aquaria were supplemented with a mixture of soybean and yeast (0.5 g 10−6 individual−1 24-h−1) as a feed source. The highest significant population growth and population growth rate of O. nana were achieved with a salinity level of 20 ppt. Regarding population composition, O. nana cultured at the salinity level of 20 ppt recorded the highest significant percentages of copepodite and nauplii. The results concluded that copepod, O. nana, is capable of withstanding abrupt changes in the salinity, but there are limits to their tolerance, with an optimal salinity level of 20 ppt. This salinity level achieved the highest population growth and the highest percentages of copepodite and nauplii of marine Copepoda, O. nana.

Optimization of salinity levels for the culture of cyclopoid copepod Dioithona oculata (Farran, 1913) with respect to total population, reproduction, development and adult longevity

“…At 15 ppt and 45 ppt, the percentage composition of adults and copepodites was higher due to the lack of naupliar production and poor survival rate. This also supports the findings of Magouz et al (2021), where a significantly higher percentage composition of nauplii and copepodites is reported in O. nana at the salinity levels from 20 to 30 ppt. There are various reports suggesting that higher the number of nauplii in a culture reflects the higher reproductive rate of the females which consequently enhances the final population (Vanderlugt et al, 2009; Wilson et al, 2021).…”

“…Nauplii of other cyclopoids like Dioithona rigida (Santhanam et al, 2018) and Oithona simplex (Noor et al, 2018) were reported to give better survival in lower salinities than the higher salinity ranges from the mean seawater salinity (35 ppt). Cyclopoids, particularly the members of Oithona and Dioithona , have better survival in lower salinities (Magouz et al, 2021). Salinity stress induces the degradation of more amino acids to meet the energy requirements for osmoregulation which in turn causes depletion in protein reserves and thereby adversely affects the survival of nauplii, especially the non‐feeding initial naupliar stages (Farmer & Reeve, 1978; Kimmel & Bradley, 2001).…”

“…Even though, most of the cyclopoid copepods survive in a euryhaline environment, their productivity varies with the changes in salinity (Pan et al, 2016). In Oithona nana , the total population was maximum at a salinity of 20 ppt (Magouz et al, 2021) and in O. rigida , the maximum production was observed at a range from 28 to 34 ppt (Santhanam & Perumal, 2012).…”

“…In Oithona nana, the total population was maximum at a salinity of 20 ppt (Magouz et al, 2021) and in O. rigida, the maximum production was observed at a range from 28 to 34 ppt (Santhanam & Perumal, 2012). Salinity changes also affected the population composition of D. oculata.…”

Influence of Microalgae Diets on the Biological and Growth Parameters of Oithona nana (Copepoda: Cyclopoida)

“…It is capable of consuming phytoplankton, bacteria, protozoa, and small crustaceans [ 47 , 48 ]. It can also consume yeast and flour from vegetable sources [ 7 , 46 , 49 , 50 ].…”